Inherits: If T is a (possibly cv-qualified)
function type then inherits from true_type,
otherwise inherits from false_type.
Note that this template does not detect pointers to functions,
or references to functions, these are detected by is_pointer and is_reference respectively:

typedefintf1();// f1 is of function type.
typedefint(f2*)();// f2 is a pointer to a function.
typedefint(f3&)();// f3 is a reference to a function.

C++ Standard Reference: 3.9.2p1 and 8.3.5.

Header:#include<boost/type_traits/is_function.hpp>
or #include<boost/type_traits.hpp>